Orifice valves generally comprise a stationary disk and a rotatable disk mounted in face-to-face engagement across a fluid path in a valve body. Each disk has at least one hole or orifice.
The rate of flow through the orifice valve is in part determined by the number and size of holes in both the stationary disk and the rotatable disk and in the degree of alignment between those holes. The degree of alignment can be changed by angular movement of the rotatable disk. This is accomplished by turning a handle, outside of the valve body, which is coupled to the rotatable disk. The rotatable disk can be moved from a fully closed position for blocking flow through the valve to a fully opened position for providing maximum flow through the valve.
Orifice valves are particularly useful for controlling the flow of fluids produced from oil and gas wells and the like. For example, orifice valves are used to control the rate of flow of well production fluids through a flow line. Often, such fluids contain abrasive materials, such as sand particles, and are under extreme pressures. For example, a pressure of the fluid entering the valve of 3,000 psi is not uncommon.
The disks divide the fluid path within the valve body into an upstream chamber and a downstream chamber. The openings in the disks are of a smaller cross-sectional area than either the upstream chamber or the downstream chamber and, as a result, the fluid accelerates as it passes through the openings in the disks. Such an increase in velocity causes the disks to wear at a faster rate than the portion of the valve body upstream from the disks. The wall of the valve body downstream from the disks also tends to wear more rapidly than the wall of the valve body upstream from the disk because, when holes in the upstream disk and downstream disk are in partial alignment, the fluid flowing through the disks is directed toward the wall of the downstream chamber rather than along its length. As a result, the fluid impinges on the wall of the downstream chamber and abrasive material in the fluid erodes the wall.
To reduce erosion or wear, the disks are typically made of erosion resistant materials such as ceramic materials, e.g., aluminum oxide, or tungsten carbide. To reduce wear of the valve body downstream from the disks, a sleeve made of erosion resistant materials, such as tungsten carbide, is inserted into and lines the downstream chamber. However, in applications such as controlling the flow of well production fluids, the fluids are sufficiently abrasive to cause erosion of such disks and protective sleeves.
To avoid the replacement of the entire orifice valve, which is both time-consuming and expensive, the orifice valves are generally designed so that the disks and the protective sleeve are replaceable. Typically, the disks are fixedly mounted in upstream and downstream annular rings, generally referred to as disk carriers, e.g., as described in U.S. Pat. No. 3,207,181.
The downstream disk carrier generally extends the length of the downstream chamber between the protective sleeve and the wall of the valve body. In this arrangement, the downstream disk is fixedly mounted in the upstream end of the downstream disk carrier and the protective sleeve is inserted into the portion of the downstream disk carrier downstream from the disk. This forms a single unit which can be easily inserted and removed from the valve body. To prevent rotational movement of the downstream disk, the downstream disk carrier comprises a slot or notch which engages a boss or the like in the valve body.
To rotate the upstream disk, orifice valves typically comprise a forked turning member. Such a turning member has a shaft extending through the valve body and a pair of tines which extend to a position adjacent the upstream disk. A handle is at the end of the shaft for rotating the turning member.
The upstream disk is fixedly mounted in the upstream disk carrier which typically comprises a pair of slots or notches which engage the tines of the turning member so that when the turning member is rotated, the upstream disk carrier and, hence, the upstream disk is rotated.
The disk carriers are typically not subject to the same amount of erosive forces as the disks and, hence, are typically made of different and less expensive materials than the material of the disks. Various means, e.g., press fitting, suitable adhesives, braying, etc., are used to fixedly mount the disks in the disk carriers. However, in addition to requiring time and manpower to mount the disks in the disk carriers, the means for joining the disks and disk carriers occasionally fail, requiring a shutdown for their replacement.